Incandescent-fluorescent lamp



July 21 1970 s, c. PEEK, JR 3,521,122

INCANDESCENT-FLUORESCENT LAMP Filed July 5, 1967 SANDFORD c. PEEK JR INVENTOR AT ORNEY United States Patent US. Cl. 31599 4 Claims ABSTRACT OF THE DISCLOSURE A combined fluorescent and incandescent lamp for use in automotive lighting is described, together with a circuit for operating it. At ordinary temperatures the light is fluorescent supplemented by some incandescent, but at low temperatures where the vapor pressure in the fluorescent lamp is low, the lighting is mostly incandescent. The lamp has two filaments at each end, one filament being coated with alkaline earth oxides for good electron emission, the other being uncoated and designed for operation at a higher temperature to enhance its incandescent light output. The lamp is preferably operated at a high frequency, for example, 20 kilocycles for the electric discharge in its fluorescent portion, and from a direct current source such as a battery or generator for its filaments. A choke coil connects an end of each filament to an end of the other for such D.C. heating, the coil preventing passage of the alternating current through itself, thus keeping it out of the filament circuits. A.C. heating of the filaments can be used if a suitable source is available, but since in an automobile the alternating current generally comes from an oscillator operating from the usual 12-volt battery, so it is preferable to make the oscillator as small as possible and operate the filaments directly from the battery.

SUMMARY OF INVENTION Field of invention This invention relates to electric lighting, especially for automobiles or in places whose ambient temperature varies widely and becomes low enough at times to dim or extinguish the usual vapor discharge, such as that in a fluorescent lamp. The invention also relates to circuits for operating such lamps under such conditions.

Summary of prior art Fluorescent lamps are well known, and their diffuse light is desirable in illuminating the interiors of automobiles, where they can be placed in coves and used for indirect lighting Where convenient. However, the usual fluorescent lamp utilizes an electrical discharge in mercury vapor for exciting the fluorescent material, usually called a phosphor, and at the low temperatures in which automobiles may be operated in the winter, especially when the car is first started and before the heating begins to take effect, or in the absence of sufiicient heating, the vapor pressure in the lamp is too low for the discharge to be efficient, with the result that the illumination will be very dim. This had prevented the use of fluorescent lighting in ordinary pleasure vehicles.

Brief summary of the invention I have found that the dimness of the illumination at low temperatures can be overcome by placing an incandescent filament in the lamp to provide illumination when the fluorescence is ineffective. The filament can be placed at an end of the lamp, or at both ends, in the vicinity of the filamentary cathodes which are usually present, and the fluorescent coating will diffuse the light throughout "ice most of the lamp. The latter, of course, will generally be tubular, but ordinarily shorter than the long 4-foot fluorescent lamps generally used for commercial lighting.

The incandescing filaments can be placed in shunt to the usual cathode filaments of the lamp. If desired, provision can be made for switching them out during normal operation of the lamp, although I prefer to simply have both incandescent and cathode filaments in shunt, being connected across the same lead-in wires, to simplify the lamp and its connections. The incandescent filament can be designed to operate at a higher temperature than the cathode filament when both are connected to the same lead-in wires. The filaments could also be placed in series, with one designed to operate at higher temperatures than the other at a lower value.

The incendescing filament can be placed behind the cathode filament, that is nearer to the end of the lamp and out of the discharge path between the cathode filaments, in order to avoid interfering with the discharge or being disintegrated by it. For this purpose the incandescible filament should be placed outside of the region of the cathode glow around the cathode filament. The latter filament will be coated with an electron emissive material such as the oxides of calcium, strontium and barium; the incandescent filament should be uncoated for best results.

The cathode filament can also act as the incandescent one itself, by running it at a somewhat higher temperature than usual, but it will then lose its coating at a more rapid rate, shortening the life of the lamp. However, the usual extremely long life of a fluorescent lamp is not necessary in automotive use, especially for interiors, where the lights would only be used occasionally.

Where an incandescent filament other than the cathode is used, it can be operated at a temperature lower than normal, in order to increase its life to a value nearer than that which the fluorescent lamp would be required to have in automotive use. The absence of the high pressure gas used in most ordinary incandescents would tend to shorten the life of the filament if it were operated at the high temperatures of a gas-filled incandescent lamp.

Actually, for automobile use the life needed is only between about and 1000 hours, generally the lower value, so the dilference in life between the discharge cathode and the incandescent filament is not important in that use.

In an automobile, the lamp filaments and cathodes can be operated from the usual storage battery of, say, twelve volts, and the power for the discharge between the cathodes supplied by an oscillator operated from the same battery. The frequency of the oscillator is not critical, but I prefer to operate it at about 20,000 cycles per second. At that frequency, the efiiciency of the lamp is high, and there will be no need for the usual currentlimiting choke coils, in series with the lamp if the oscillator is designed to operate the lamp at the correct current. A choke coil is, however, connected between the two filaments in series to allow the direct current to pass to heat the filaments, while excluding the high-frequency oscillator current from the filament heating circuit. A choke coil can also be used in series with one terminal of the battery itself to keep the oscillator current out of the battery.

BRIEF DESCRIPTION OF DRAWINGS Other objects, features and advantages of the invention will be apparent from the following specification, taken in connection with the accompanying drawings, in which:

FIG. 1 is a schematic drawing of a lamp according to the invention in a suitable circuit; and

FIG. 2 is a schematic drawing of a lamp in another suitable circuit.

DESCRIPTION OF SPECIFIC EMBODIMENTS In FIG. 1, the fluorescent lamp 1 has the glass envelope 2, coated on its interior with the fluorescent phosphor coating 3, and containing the usual inert gas and mercury, the lead-in wires 4, 5, 6, 7 at each end of the envelope being connected to and supporting the cathodes 8, 9 and the incandescent filaments 10, 11. Each incandescent filament is a coiled-coil of tungsten wire, adapted to operate at incandescence to produce visible light, one end of each wire being connected to lead-in wire 4 and the other end to lead-in wire 5. Between these two wires is also connected the cathode 8 which is a coiled-coil tungsten wire coated in the usual manner with oxides of barium, strontium and calcium to facilitate electron emission. The cathode 9 and the incandescent filament at the other end are connected in the same manner between the lead-in wires 6 and 7. Lead-in wires 4 and 6 are connected together through a choke coil or inductance 12. The inductance should be sufficient to prevent passage of the alternating current from the oscillator 13, which is connected in series with lead-in wire 7 through the trans former 17. The other end of the secondary coil 14 of transformer 17 is connected to one terminal of the battery 15, the other terminal of said battery being connected to a lead-in wire 5. The primary 16 of transformer 17 is connected to the oscillator 13.

In operation the battery 15 heats the cathode 8 which is connected in series with the battery and with the inductance 12 and also heats the filament 10 to incandescence. The alternating voltage supplied by the oscillator 13 produces an electrical discharge between the cathodes 8 and 9 through the gas and vapor in the tube 2. This discharge excites the fluorescent coating 3 to emit light in the usual manner. However, if the temperature is too low for the mercury to be vaporized sufiiciently to sustain the discharge, there will still be a considerable amount of light from the incandescent filaments 10, 11 and this light will be diffused by the fluorescent coating 3. The oscillator 13 may be one of the usual types operable from the battery 15. The two grounds 18 and 19 are in effect simply a means of connecting one end of the battery to the transformer, completing the circuit.

In FIG. 2, the set-up is the same except for the connections of oscillator 13 and the battery 15. In this case the oscillator 13 is connected directly across lead-in wires 5 and 7 to produce an electric discharge between cathodes 8 and 9. The transformer 17 is omitted. The battery is then connected in shunt to the oscillator through the choke coil 20 which prevents the alternating current from the oscillator from flowing through the battery 15. Otherwise the operation is the same. The choke 12 can be wound on the same core with transformer 17.

Although certain specific embodiments of the invention have been described herein various modifications thereof will be apparent to a worker skilled in the art upon reading this specification, without departing from the spirit and scope of the invention which is set forth in the claims.

What I claim is:

1. A circuit for a fluorescent lamp having at least two sets of filaments between which sets an electrical discharge is to be passed, said circuit comprising an inductance coil connecting one end of each set of filaments together, and a battery and secondary of a transformer in series across the other ends of each set of filaments, and an oscillator connected to the primary of said transformer, the inductance passing direct current but opposing passage of alternating current from said oscillator.

2. A circuit for a fluorescent lamp having at least two sets of filaments between which sets an electrical discharge is to be passed, an inductance coil connecting an end of each set of filaments together, an oscillator connected to the other ends of said sets, and a battery in series with an inductance coil also connected to said other ends, said inductance coils passing direct current from the battery but opposing passage of alternating current from the oscillator.

3. A fluorescent lamp circuit comprising a fluorescent lamp having an enclosing envelope, a gas filling therein, a vaporizable material therein, a phosphor coating on the interior of said envelope, and two sets of filaments in said envelope, said sets being spaced apart, each set containing one incandescible filament and one cathode filament, only the latter filament being coated with electron-emitting material, said incandescible filament being designed to operat at higher temperature than said cathode filament in order to provide incandescent light while the vaporizable material is warming up, in combination with an inductance coil connecting an end of each set of filaments together, an oscillator connected to the other ends of said sets, and a battery in series with an inductance coil also connected to said other ends, said inductance coils passing direct current from the battery but opposing passage of alternating current from the oscillator.

4. A fluorescent lamp circuit comprising a fluorescent lamp having an enclosing envelope, a gas filling therein, a vaporizable material therein, a phosphor coating on the interior of said envelope, and two sets of filaments in said envelope, said sets being spaced apart, each set containing one incandescible filament and one cathode filament, only the latter filament being coated with electronemitting material, said incandescible filament being de signed to operate at higher temperature than said cathode filament in order to provide incandescent light while the vaporizable material is warming up, in combination with an inductance coil connecting one end of each set of filaments together, and a battery and secondary of a transformer in series across the other ends of each set of filaments, and an oscillator connected to the primary of said transformer, the inductance passing direct current but opposing passage of alternating current from said oscillator.

References Cited UNITED STATES PATENTS 2,315,286 3/1943 Hays 313-1 X 2,429,415 10/1947 Lemmers 315--99 2,964,676 12/ 1960 Davies 31598 3,215,881 11/1965 Waymouth 313-216 X 3,412,276 11/1968 Curl 313109 X FOREIGN PATENTS 1,295,408 5/ 1962 France.

JAMES W. LAWRENCE, Primary Examiner E. R. LAROCHE, Assistant Examiner US. Cl. X.R. 

